The fabrication of semiconductor devices, such as logic and memory devices, typically includes processing a semiconductor device using a large number of semiconductor fabrication processes to form various features and multiple levels of the semiconductor devices. Some fabrication processes utilize photomasks/reticles to print features on a semiconductor device such as a wafer. As semiconductor device size becomes smaller and smaller, it becomes critical to develop enhanced inspection and review devices and procedures to increase the resolution, speed, and throughput of wafer and photomask/reticle inspection processes.
One inspection technology includes electron beam based inspection such as scanning electron microscopy (SEM). In some instances, scanning electron microscopy is performed by splitting a single electron beam into numerous beams and utilizing a single electron-optical column to individually tune and scan the numerous beams (e.g., a multi-beam SEM system). However, splitting a beam into an N number of lower-current beams traditionally reduces the resolution of the multi-beam SEM system, as the N number of beams are tuned on a global level and individual images cannot be optimized. Additionally, splitting a beam into an N number of beams results in needing more scans and averages to obtain an image, which reduces the speed and throughput of the multi-beam SEM system. Further, multi-beam SEM systems have scalability constraints, where issues such as field curvature and other transverse aberrations become harder to correct as the size of the multi-beam SEM systems increases. Further, multi-beam SEM systems have issues with crosstalk between electron detectors within the systems, which is difficult to reduce and/or otherwise control without reducing secondary electron collection efficiency. Reducing crosstalk requires a high extraction field and a high secondary electron beam kinetic energy.
In other instances, scanning electron microscopy is performed via secondary electron beam collection (e.g. a secondary electron (SE) imaging system). However, these SE imaging systems are traditionally relatively large in size, the size being necessary to support the high voltages required to limit the SE imaging system to manageable chromatic aberration contributions. Additionally, the secondary electron collection efficiency of the SE imaging systems is low compared to other SEM system architectures (e.g. multi-beam or multi-column SEM systems). Further, the current per imaging pixel is low, so the intrinsic collection/exposure time per imaging pixel must be increased to compensate for the low current. Further, an SE imaging system requires a high extraction field, similar to the multi-beam SEM system.
In other instances, scanning electron microscopy is performed via an SEM system which includes an increased number of electron-optical columns (e.g. a multi-column SEM system). Traditionally, these electron-optical columns are individual stacks of metal, ceramic rings, and electromagnets. These individual stacks are too large to be placed together with an ideal pitch for optimizing wafer or photomask/reticle scan speed, and cannot be miniaturized to allow for packing a significant number of electron-optical columns in a usable area, resulting in a limitation of the number of stacks in the multi-column SEM system (e.g. four stacks). Additionally, having individual stacks results in issues with electron-optical column matching, crosstalk between the columns, and errant charging. Further, condensing and focusing is achieved for each electron-optical column through electrostatic means, which requires either the use of high-voltage gradients or a limitation in the physical scale reduction of the electron-optical columns. Both the use of high-voltage gradients and limiting the physical scale reduction presents risks of arcing or micro-discharge noise.
Therefore, it would be advantageous to provide a system that cures the shortcomings described above.